Manna S K, Mukhopadhyay A, Aggarwal B B
Cytokine Research Laboratory, Department of Bioimmunotherapy, University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
J Immunol. 2000 Nov 15;165(10):5962-9. doi: 10.4049/jimmunol.165.10.5962.
Leflunomide is a pyrimidine biosynthesis inhibitor that has recently been approved for treatment of rheumatoid arthritis. However, the mechanism of leflunomide's antiarthritis activity and is not fully understood. The critical role that TNF plays in rheumatoid arthritis led us to postulate that leflunomide blocks TNF signaling. Previously, we have demonstrated that leflunomide inhibits TNF-induced NF-kappaB activation by suppressing I-kappaBalpha (inhibitory subunit of NF-kappaB) degradation. We in this study show that leflunomide also blocks NF-kappaB reporter gene expression induced by TNFR1, TNFR-associated factor 2, and NF-kappaB-inducing kinase (NIK), but not that activated by the p65 subunit of NF-kappaB, suggesting that leflunomide acts downstream of NIK. Leflunomide suppressed TNF-induced phosphorylation of I-kappaBalpha, as well as activation of I-kappaBalpha kinase-beta located downstream to NIK. Leflunomide also inhibited TNF-induced activation of AP-1 and the c-Jun N-terminal protein kinase activation. TNF-mediated cytotoxicity and caspase-induced poly(ADP-ribose) polymerase cleavage were also completely abrogated by treatment of Jurkat T cells with leflunomide. Leflunomide suppressed TNF-induced reactive oxygen intermediate generation and lipid peroxidation, which may explain most of its effects on TNF signaling. The suppressive effects of leflunomide on TNF signaling were completely reversible by uridine, indicating a critical role for pyrimidine biosynthesis in TNF-mediated cellular responses. Overall, our results suggest that suppression of TNF signaling is one of the possible mechanisms for inhibitory activity of leflunomide against rheumatoid arthritis.
来氟米特是一种嘧啶生物合成抑制剂，最近已被批准用于治疗类风湿性关节炎。然而，来氟米特抗关节炎活性的机制尚未完全明确。肿瘤坏死因子（TNF）在类风湿性关节炎中起关键作用，这使我们推测来氟米特可阻断TNF信号传导。此前，我们已证明来氟米特通过抑制I-κBα（NF-κB的抑制亚基）降解来抑制TNF诱导的NF-κB活化。我们在本研究中表明，来氟米特还可阻断由TNFR1、TNFR相关因子2和NF-κB诱导激酶（NIK）诱导的NF-κB报告基因表达，但不能阻断由NF-κB的p65亚基激活的报告基因表达，这表明来氟米特作用于NIK的下游。来氟米特抑制TNF诱导的I-κBα磷酸化以及位于NIK下游的I-κBα激酶-β的活化。来氟米特还抑制TNF诱导的AP-1活化和c-Jun N末端蛋白激酶活化。用Jurkat T细胞处理来氟米特也可完全消除TNF介导的细胞毒性和半胱天冬酶诱导的聚（ADP-核糖）聚合酶裂解。来氟米特抑制TNF诱导的活性氧中间体生成和脂质过氧化，这可能解释了其对TNF信号传导的大部分作用。来氟米特对TNF信号传导的抑制作用可被尿苷完全逆转，表明嘧啶生物合成在TNF介导的细胞反应中起关键作用。总体而言，我们的结果表明，抑制TNF信号传导是来氟米特对类风湿性关节炎抑制活性的可能机制之一。
